The recent case of a highly infectious tuberculosis patient who crossed international borders on two different flights has many travelers wondering… how protected are you from disease when you fly?

Andrew Speaker, a 31-year-old Atlanta attorney, suffers from extremely drug-resistant tuberculosis (XDR-TB). Although advised not to travel, Speaker flew to Paris on May 12 aboard Air France 385/Delta 8517 from Atlanta. He then traveled Greece to be married, and then to Rome for his honeymoon, where he was contacted by the CDC and urged to report to Italian authorities for treatment.

The couple went to Prague and flew to Montreal on Czech Air 0104 on May 24. They entered the U.S. in Champlain, New York by rented car, despite the fact that his passport was flagged on the U.S. Customs and Border Patrol’s computer system.

The World Health Organization (WHO) pamphlet “Tuberculosis and Air Travel: Guidelines for Prevention and Control,” strongly advises that “persons known to have infectious TB should remain in isolation at home or at hospital, depending on the policies of the national programme, until no longer infectious. When travel is necessary while a person is still infectious, commercial carriers or other public transportation should not be used. Alternative private transportation (e.g. ground transportation, air ambulance, etc.) could be used instead.”

Also according to the WHO, all new commercial jet aircraft recirculate air, and many older aircraft built before the late 1980s have been retrofitted to do so. About 10%-50% of cabin air is filtered, mixed with fresh air and reintroduced into the cabin. “Generally, the first filter traps the largest particles. On most modern aircraft, before re-entering the passenger cabin, the air passes through a high-efficiency particulate air (HEPA) filter, which can capture material as small as 0.3 microns.” Tuberculosis bacteria is about 0.5 to 1 micron in size.

Although there is no definition of what is a “modern aircraft,” Czech Air 0104 is an Airbus A310 that had its maiden flight in 1982. Air France 385 is a Boeing 747-400, which first entered service in February 1989. Representatives at Boeing have confirmed that this aircraft is supplied with HEPA filters, and state that all aircraft currently in production include these air filters.

Dr. Julie Gerberding, director for the Centers for Disease Control (CDC), has said that the passengers most likely to be at risk would be those who were in seats immediately close to the patient–those in the same row, and two rows ahead and behind him. According to the CDC, the highest priority subjects are those passengers seated in rows 28-32 on the Air France flight and those seated in rows 10-14 on the Czech Air flight, as well as flight crew members working in the same cabin on those two flights.

“We have no suspicion that this patient was highly infectious, in fact medical evidence would suggest that his potential for transmission would be on the low side,” cautions Dr. Gerberding.

Tuberculosis is a bacterial infection that usually attacks the lungs. It is spread through the air and can lead to symptoms such as chest pain and coughing up blood. There were an estimated 1.6 million deaths from TB in 2005, according to the World Health Organization (WHO). There have been 17 U.S cases of the extremely drug resistant TB since 2000, according to the CDC. This rare form of tuberculosis means the disease is resistant to the two first-line antibiotics that are commonly used for treatment: isoniazid and rifampin, and at least one of three second-line drugs.

According to Dr. Harry Conte, who specializes in infectious diseases and internal medicine at St. Francis Hospital in Connecticut, tuberculosis “spreads into your body and sets up shop. You don’t necessarily get the disease–there is a 5% risk of developing the lung disease over the course of two years. After those two years there is another 5% chance in your lifetime.”

However, he does point out that if your immune system is compromised, particularly with HIV/AIDS, your likelihood of developing active tuberculosis is about 40% over the course of a few months. According to Dr. Conte, tuberculosis was on the decline for years due to antibiotics and other measures, but resurfaced around 1985, most likely due to the HIV/AIDS epidemic.

Dr. Conte states that being on an airplane with someone who has a contagious disease such as tuberculosis is “about as infectious as being in a room with someone. Unless the airline is using a HEPA filter, if a person is coughing, it would eventually contaminate the entire plane.”

He points out that someone who is infected with lung lesions, or cavities, is likely to be far more infectious than someone like Mr. Speaker who is considered to be asymptomatic. “The real surprise is that he’s not sick. Usually people that have extreme drug resistant are usually very sick with the disease. You wouldn’t be thinking about whether or not you should travel–you wouldn’t even be thinking about getting out of bed.”

The larger concern for many travelers is not the spread of tuberculosis from this incident, but how this passenger was able to exit and re-enter the country despite the fact that his passport was flagged. U.S. Customs and Border Protection was informed by the CDC that the passenger (patient) had a highly infectious disease. A warning was issued that agents should “isolate, detain or call the public health service” if Speaker tried to cross the border. Human error and poor judgment is being blamed, as it’s believed that an agent at the border crossing in New York let him through because he didn’t appear to be ill.

Rep. Bennie Thompson (D-Mississippi), Chairman of the House Committee on Homeland Security, has scheduled a hearing for Wednesday, June 6 to look into whether the government agencies were communication properly. The hearing, to be held at 10 a.m. (EST) is entitled “The XDR Tuberculosis Incident: A Poorly Coordinated Federal Response to an Incident with Homeland Security Implications.” Witnesses will include members of the Department of Homeland Security, U.S. Customs and Border Security, and potentially Dr. Gerberding from the CDC. This hearing will be webcast live.